FIG. 1 illustrates a known way to connect a string 10 to a packer P via a packer extension 12. Extension 12 has a polished seal bore 14 against which a seal stack 16 is positioned. When the seal stack 16 is in position a thread 18 is made up. This thread makeup also secures the position of a metal to metal seal 20 against the surrounding extension 12. A left hand square thread 18 is exposed when string 10 is rotated to undo thread 18 and a release tool of a known design is run in and engaged to thread 18. The release tool that is not shown also engages a sleeve on the packer to release the packer upon application of an uphole force. The seal stack 16 is intended to be a backup to the metal to metal seal 20. The issue with this design is that operators are disinclined to rely on a seal stack for a backup. The presence of a seal stack requires a different and more complex testing regimen. The other potential issue with this design is that the metal to metal seal 20 under severe thermal and/or tensile loads could lose its seal and the operators were leery of falling back on the seal stack for a secure connection that would not leak.
More recently an improved design was published as US 20180128059. For context in understanding the present invention, FIG. 2 is from that application that is commonly assigned to the same assignee, Baker Hughes Incorporated and has common inventorship. FIG. 2 shows a packer extension 30 engaged by a string 32 at thread 34. There is no seal bore just a metal to metal seal in the form of thread 34. Release of the packer P requires undoing thread 34 and removing the string 32 followed by running in a release tool to engage left handed square thread 36 with a known release tool that grabs a sleeve on the packer P in a known way to release it so that the packer and extension 30 come out together with the release tool engaged to thread 36. This novel design eliminated the need for a seal bore and addressed the operator concern of the metal to metal seal 20 losing its seal under extreme conditions as described above. However, operators raised a new concern with regard to the unique FIG. 2 design in that there could be situation where the torque required to release the threaded connection 34 could be higher than equipment capability from the surface to unthread or even worse the torque applied could be so high that the tubular string could shear at or outside the thread 34 which could cause an expensive fishing or milling operation to be undertaken.
The present invention overcomes the operator concern to the FIG. 2 design and provides a release from the packer with a mandrel sever above the metal to metal threaded connection. This cutting allows for string removal and exposes a left handed square thread that can then be engaged by a known packer release tool for release and removal of the packer with the release tool. No rotation is needed for the release of the original string from the packer. These and other aspects of the present invention will be more readily understood by a review of the description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be determined by the appended claims.